Tartrate-resistant acid phosphatase (TRAP) is expressed at high levels in osteoclasts and may play an important role in the bone resorptive process. However, factors regulating human TRAP gene expression have not been clearly defined. Therefore, we isolated a genomic clone (CL-9) for TRAP containing a 14-kb insert. A restriction map was generated for this insert, and a 2.6-kb Apal fragment containing the 5′-flanking region was subcloned. Sequence analysis of this fragment revealed the presence of candidate transcription factor-binding sequences for H-APF-1, SP1, GATA2, and the c-Myc proto-oncogene. PCR analysis of RNA isolated from human osteoclastomas and pagetic bone revealed a 276-bp intron at −1 by to −276 bp relative to the ATG and a transcript originating from this intron. Rapid amplification of the 5′ end of the human TRAP mRNA by PCR indicated the presence of a 93-bp untranslated region 5′ from the intron. Promoter activity was detected in the DNA fragment from +1 bp to −1903 by relative to the ATG initiation codon, which drove the transient expression of a luciferase reporter gene when transfected into HRE H9 rabbit endometrial cells. Comparison of the human TRAP 5′-flanking region with mouse TRAP and uteroferrin revealed 41% and 47% homology, respectively. This suggests that regulation of human TRAP gene expression may differ from that for the murine TRAP gene.